Just three hours later, another bullet fired into the air in celebration of the new year penetrated the skull of a 12-year-old boy in Ruskin, critically wounding him.

Police say Harker, 41, of St. Petersburg was lucky to avoid a similar fate. But authorities will have a tough time solving either crime.

Celebratory gunfire is random and without a motive or connection, so the pool of possible suspects is huge. There just isn't much to go on, said Gulfport Lt. Howard Coombs.

In Harker's case, authorities say they have the bullet, a .45-caliber slug. Hillsborough County deputies don't even have that.

The bullet that hit Diego Duran, 12, remained lodged behind his cheekbone Tuesday. Doctors don't want to remove it until he has stabilized and the swelling in his head has decreased, his mother said Monday.

This type of crime rarely results in an arrest. But Hillsborough authorities are still trying.

In some ways, it's like a hit-and-run investigation, said Hillsborough sheriff's spokesman Larry McKinnon.

Both crimes are random, which means many suspects and no motives. So detectives rely largely on tipsters.

They need someone to name a neighbor who was firing a gun at that time. Or someone to say a co-worker mentioned it could be his or her fault.

But just because a person was firing a gun in the area doesn't guarantee it shot the bullet that hit Diego as he watched fireworks with his family at their home, near the intersection of U.S. 41 and College Avenue.

The bullet has to match.

State ballistics experts can match a gun with the bullet — similar to comparing a suspect's damaged car with paint chips found at a hit-and-run scene. But they need the bullet and gun.

The bullet could provide another clue: It could give detectives a better idea how far away the gun was fired, said ballistics expert Ronald Scott.

Hillsborough deputies believe the bullet that hit Diego could have come from up to 3 miles away. Scott, who ran a ballistics lab with the Massachusetts State Police and now serves as a gun expert, says that's possible — with a rifle.

If the bullet is from a pistol, it likely came from within a 1-mile radius, he said.

"It can't go that far," he said. "There's not enough speed, it doesn't weigh enough and (pistol bullets) have air resistance that make them fall to the ground."

Though X-rays show a metal object that deputies are certain is a bullet, they can't tell what caliber it is or whether it came from a rifle or pistol, McKinnon said.

But deputies are certain it fell because of a New Year's Eve ritual that has been going on for decades.

Scientists have studied the phenomenon of deadly "celebratory" fire for years. Several studies were prompted by the deaths of 20 Kuwaitis from falling bullets at the end of the Persian Gulf War.

Though research has shown that the terminal velocity of a bullet fired 90 degrees into the air likely wouldn't penetrate a skull, a bullet fired at a different angle can have enough velocity and kinetic energy to kill — even as it descends along an arching trajectory. A velocity of less than 200 feet per second can fracture bone, and bullets can reach up to 600 feet per second on downfall, according to a 2007 article in the Annals of Thoracic Surgery.

Nationwide, it's a deadly tragedy that is fatal at a higher rate than shootings in general, according to a 1994 study in the Journal of Trauma.

That is because the bullets are coming from above and are most likely to hit people in the head — 77 percent of the time, according to the study.

That's where Diego was hit, deputies say. The bullet traveled through the front of his brain and stopped behind his cheekbone. He was in serious condition Tuesday.

The Hillsborough County Sheriff's Office is still seeking tips on who was firing a gun into the sky in Ruskin about 1 a.m. Sunday. Anyone with information can call the Sheriff's Office at (813) 247-8200 or Crime Stoppers toll-free at 1-800-873-8477.

Times news researcher John Martin contributed to this report. Jessica Vander Velde can be reached at jvandervelde@tampabay.com or (813) 226-3433.